Hi all,
I tried unsuccessfully to publish experiments showing this bug in Moses behaviour. As a result I have lost interest in attempting to have my work published. Nonetheless I think you all should be aware of an anomaly in Moses' behaviour which I have thoroughly exposed and should be easy enough for you to reproduce. As I understand it the TM logic of Moses should select the most likely translations according to the TM. I would therefore expect a run of Moses with no LM to find sentences which are the most likely or at least close to the most likely according to the TM. To test this behaviour I performed two runs of Moses. One with an unfiltered phrase table the other with a filtered phrase table which left only the most likely phrase pair for each source language phrase. The results were truly startling. I observed huge differences in BLEU score. The filtered phrase tables produced much higher BLEU scores. The beam size used was the default width of 100. I would not have been surprised in the differences in BLEU scores where minimal but they were quite high. I have been unable to find a logical explanation for this behaviour other than to conclude that there must be some kind of bug in Moses which causes a TM only run of Moses to perform poorly in finding the most likely translations according to the TM when there are less likely phrase pairs included in the race. I hope this information will be useful to the Moses community and that the cause of the behaviour can be found and rectified. James
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